Page 633 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 28 Tumors of the Mammary Gland 611

stage I, smaller than 3 cm; stage II, between 3 cm and 5 cm; and dogs treated at a single institution found no difference in DFI or
stage III, larger than 5 cm. 124,140 Dogs with stage I tumors have a OST compared with the type of surgical procedure performed,
Others, however, have found
whether lumpectomy, local mastectomy, regional mastectomy
significantly longer survival.
13,74,141
VetBooks.ir that a change in prognosis only becomes significant when tumors with en bloc LN excision, or chain mastectomy with en bloc LN
excision.
29,142
are larger than 5 cm.
However, the relative hazard for death within the
The change in prognosis is likely gradual
143
as tumors increase in size. The modified WHO staging system has first 2 years after surgery was slightly higher for dogs receiving a
incorporated these three size categories representing stage I, stage regional mastectomy over a chain mastectomy. 143 Interestingly,
II, and stage III disease, respectively. 125 Importantly, however, the in one study, the hazard curves for DFI and survival were quite
size of the tumor becomes irrelevant if the local LN is involved. similar, suggesting that most dogs that experienced recurrence
13
A positive LN constitutes stage IV disease according to the revised developed metastasis and not new tumors; however, the rate of
WHO system, attributing a worse prognosis to LN involvement new tumors was not reported in this study. 140 A different study
rather than tumor size. indicated that surgical “dose” is important. In this case series
of 99 dogs, all intact female dogs underwent either a regional
Lymph Node Status or chain mastectomy for a single MGT with unknown histol-
A large retrospective study, including only dogs with carcinomas, ogy. 145 Of these, 58% of dogs developed a new tumor in the
all of which had the local or draining LN removed and biopsied, remaining ipsilateral MG tissue after a regional mastectomy and
found that the status of the local LNs was highly prognostic. those whose initial tumor was subsequently determined to be
13
Others have confirmed these findings. 29,74,77,135,138,143 Therefore malignant were more likely to develop an ipsilateral tumor. The
information regarding the status of the local LN is extremely authors advocated for an initial unilateral chain mastectomy for
important when considering the need for adjuvant or systemic female intact dogs with a single MGT, although, in their popu-
therapy in dogs with MGTs. Earlier publications did not quan- lation, 42% of dogs did not develop a subsequent tumor and
tify the extent of LN involvement or did not use IHC to facili- would have experienced a larger surgical dose than needed. 145
tate identification of microscopic clusters or isolated tumor cells, Although a more aggressive surgical approach does not affect
potentially including only dogs with macrometastasis in their MGT development in the contralateral mammary chain or
analysis. More recent publications, however, have investigated improve STs, it does decrease the need for further surgery for
the significance of microscopic LN metastasis. Micrometastasis, the management of subsequent MGTs in the ipsilateral mam-
defined as clusters of cells ranging from 0.2 to 2.0 mm in diame- mary chain in approximately 60% of dogs. It is worth noting,
ter, 116,144. did not predict a significantly worse outcome compared however, the significant incidence of postoperative complica-
with dogs with no evidence of metastasis. Interestingly, dogs with tions (77%) in dogs undergoing radical mastectomies when
isolated metastatic tumor cells (not in clusters) had a worse out- making such recommendations 146 Other large useful studies
come according to one of these studies. 144 investigating the association between OHE and survival did not
report on the completeness or extent of MGT removal. 20,147,148
WHO Staging System Development of second MGTs is well documented and has been
Both the original and the revised WHO staging system pro- reported in more than 70% of dogs with malignant MGTs after
vide prognostic information. When performing a side-by-side lumpectomy, although the effect of second MGT development
comparison of the two systems, the revised system appears to on survival is not well delineated. 18,140,145 It is clear from a pro-
better reflect the stronger effect of LN status on prognosis. 126 spective randomized study trial for intact dogs having benign
Nevertheless, the original staging system also provides useful MGTs that concurrent OHE significantly reduces the risk of
prognostic information as illustrated in two larger separate ret- future MGT development by almost 50% and reduces the risk
21
rospective studies in which dogs with higher WHO stage disease for additional life-threatening uterine and ovarian diseases. A
had a significantly worse prognosis than dogs with lower stage related prospective randomized clinical trial of 60 intact dogs
disease. 29,143 having malignant MGTs demonstrated that a small subset of
dogs benefited from concurrent OHE, specifically those dogs
Therapy with grade II ER+ tumors or dogs with increased peri-surgical
79
serum E 2 concentration. A single standardized guideline for
Surgical Treatment surgical treatment omits consideration of factors such as the age,
The challenge in preparing surgical recommendations is the lack tumor size, tumor number, previous MGTs, and clinical stage,
of uniform, robust prospective clinical trials that clarify the extent and may not provide the optimal outcome. Future carefully con-
or “dose” of surgical excision: simple lumpectomy, local mastec- structed clinical trials may offer more tailored recommendations
tomy, regional mastectomy, chain mastectomy, or bilateral mastec- based on the individual patient’s risk.
tomies. The goal of the surgery must be defined through staging Current recommendations based on available data suggest
and counseling with the owner. Is the goal to remove the current that for dogs with a single MGT of known or unknown his-
tumor(s) with clean margins or remove the current tumor(s) with totype, surgical excision wide enough to completely remove
clean margins and prevent new tumors in the remaining glands? the tumor is adequate. 149 Incomplete excision or cytoreductive
The latter option as elaborated in the next paragraph would procedures are not recommended. 123 Tumors that are fixed or
require prophylactic mastectomies of clinically normal glands in have skin ulceration and are less than 1 cm in diameter may
addition to affected glands. be sufficiently managed with a local mastectomy (Fig. 28.3). 123
Several studies have evaluated the effect of surgical dose in Wide excision has not been well defined, but for larger tumors,
canine mammary tumors. A prospective randomized trial of 144 this may be generalized to a 2-cm lateral margin and modified
dogs with naïve malignant tumors comparing the DFI and OST according to the size of the patient and tumor. 123 The deep mar-
benefit relative to either chain mastectomy or simple mastectomy gin may need to include the abdominal muscular fascia and/or
found no differences. 140 Similarly, a retrospective case series of 79 portions of the abdominal wall to be excised en bloc with the